Organic light emitting diode display and driving method thereof

• US 20080174574A1
• Filed: 05/26/2007
• Published: 07/24/2008
• Est. Priority Date: 05/26/2006
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Philips LCD Company Limited (LG Display Co., Ltd.)
• Inventors: Yoo, Juhn Suk
• Granted Patent: US 7,898,511 B2
• Time in Patent Office: Days
• US Class Current: 345/204
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 2310/0254 Control of polarity reversal in general, other than for liquid crystal displays
• CPC Class Codes: G09G 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element

Abstract

An organic light emitting diode display compensates for a threshold voltage of a thin-film driving transistor to improve display quality. The display includes a light emitting cell connected between a high-level voltage source and a first node. A driving transistor is connected between the first node and a ground voltage source to control a current, which flows in the light emitting cell, by using a voltage applied to a gate terminal of the driving transistor. A data driving circuit applies a data voltage of first polarity to the gate terminal of the driving transistor to shift a threshold voltage of the driving transistor from a reference value to the voltage of first polarity. A compensation circuit supplies a compensation voltage of second polarity to the gate terminal of the driving transistor to shift the threshold voltage of the driving transistor from the voltage of first polarity to the voltage of second polarity, and then supplies a constant current to the gate terminal of the driving transistor to restore the threshold voltage of the driving transistor to the reference value.

Claims

1. An organic light emitting diode display, comprising:

a light emitting cell connected between a high-level voltage source and a first node;

a driving transistor connected between the first node and a ground voltage source to control a current flow in the light emitting cell, by using a voltage applied to a gate terminal of the driving transistor;

a data driving circuit configured to apply a data voltage of first polarity to the gate terminal of the driving transistor to shift a threshold voltage of the driving transistor from a reference value to the voltage of first polarity; and

a compensation circuit configured to supply a compensation voltage of second polarity, which is different from the first polarity, to the gate terminal of the driving transistor to shift the threshold voltage of the driving transistor from the voltage of first polarity to the voltage of second polarity, wherein

the compensation circuit then supplies a constant current to the gate terminal of the driving transistor to restore the threshold voltage of the driving transistor to the reference value.

2. The organic light emitting diode display according to claim 1, wherein the compensation circuit comprises:

a bias applying source that supplies a compensation voltage of second polarity, which is different from the first polarity, to the gate terminal of the driving transistor; and

a constant current source that supplies the constant current to the gate terminal of the driving transistor.

3. The organic light emitting diode display according to claim 2, wherein the compensation circuit compares a voltage at the gate terminal of the driving transistor, which is changed as the constant current is supplied, with the reference value, and switches a current path between the constant current source and the gate terminal of the driving transistor in accordance with the comparison.

4. The organic light emitting diode display according to claim 3, wherein the light emitting cell is located in each of m×

n pixel areas defined by m data lines and 2n gate lines, and the compensation circuit restores threshold voltages of driving transistors located at k (k<

n) horizontal lines for a blank period between two vertical synchronization periods, and restores threshold voltages of all driving transistors located at the n horizontal lines for a plurality of blank periods.

5. The organic light emitting diode display according to claim 4, wherein the pixel area comprises:

a first switch transistor connected between the data line and the gate terminal of the driving transistor to control the driving transistor; and

a second switch transistor connected between the data line and the first node to short-circuit the gate terminal with a drain terminal of the driving transistor when the constant current is applied.

6. The organic light emitting diode display according to claim 5, wherein the gate line comprises:

a first gate line connected to a gate terminal of the first switch transistor; and

a second gate line connected to a gate terminal of the second switch transistor.

7. The organic light emitting diode display according to claim 6, further comprises an emission transistor connected between the light emitting cell and a source terminal of the second switch transistor.

8. A method of driving an organic light emitting diode display, the display including a light emitting cell connected between a high-level voltage source and a first node, and a driving transistor connected between the first node and a ground voltage source to control current flow in the light emitting cell by using a voltage applied to a gate terminal of the driving transistor, the method comprising:

applying a data voltage of first polarity to the gate terminal of the driving transistor to shift a threshold voltage of the driving transistor from a reference value to the voltage of first polarity;

shifting the threshold voltage of the driving transistor from the voltage of first polarity to a voltage of second polarity by supplying a compensation voltage of second polarity different from the first polarity, to the gate terminal of the driving transistor; and

restoring the threshold voltage of the driving transistor to the reference value by supplying a constant current to the gate terminal of the driving transistor from a constant current source.

9. The method of driving the organic light emitting diode display according to claim 8, wherein restoring the threshold voltage includes:

comparing the gate terminal voltage of the driving transistor, which is changed according to the constant current, with the reference value; and

switching a current path between the constant current source and the gate terminal of the driving transistor in accordance with the comparison.

10. The method of driving the organic light emitting diode display according to claim 9, wherein threshold voltages of the driving transistors located at k (k<

n) horizontal lines within an entire pixel area which is defined by m data lines and 2n gate lines are restored for a blank period defined between two vertical synchronization periods, and the threshold voltage of all the driving transistors located at the n horizontal lines are restored for a plurality of the blank periods.

11. An organic light emitting diode display, comprising:

a light emitting cell connected between a high-level voltage source and a first node;

a driving transistor connected between the first node and a ground voltage source to control a current flow at the light emitting cell, using a voltage applied to a gate terminal of the driving transistor;

a data driving circuit configured to apply a data voltage to the gate terminal of the driving transistor to increase a threshold voltage of the driving transistor to a value greater than a reference value;

a compensation circuit configured to supply a compensation voltage, which is different from the data voltage, to the gate terminal of the driving transistor to reduce the threshold voltage of the driving transistor to a value less than the reference value; and

the compensation circuit configured to supply a constant current to the gate terminal of the driving transistor to restore the threshold voltage of the driving transistor to the reference value.